The semiconductor industry has experienced rapid growth due to improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from shrinking the semiconductor process node (e.g., shrink the process node towards the sub-20 nm node). As semiconductor devices are scaled down, new techniques are needed to maintain the electronic components' performance from one generation to the next. For example, low gate-to-drain capacitance and high breakdown voltage of transistors may be desirable for power applications.
As semiconductor technologies evolve, metal oxide semiconductor field effect transistors (MOSFET) have been widely used in today's integrated circuits. MOSFETs are voltage controlled devices. When a control voltage is applied to the gate a MOSFET and the control voltage is greater than the threshold of the MOSFET, a conductive channel is built between the drain and the source of the MOSFET. As a result, a current flows between the drain and the source of the MOSFET. On the other hand, when the control voltage is less than the threshold of the MOSFET, the MOSFET is turned off accordingly.
MOSFETs may include two major categories. One is n-channel MOSFETs; the other is p-channel MOSFETs. According to the structure difference, MOSFETs can be further divided into two sub-categories, namely trench power MOSFETs and lateral power MOSFETs.
As process nodes keep shrinking, the physical size of MOSFETs is scaled down. The scaled down structure of MOSFETs may lead to the change of the electrical characteristics of MOSFETs due to short channel effects. For example, in order to obtain a low on resistance MOSFET, a shorter channel length is employed to reduce the on resistance. However, such a shorter channel length may cause the short channel effect. More particularly, as the drain region and the source region of the MOSFET get closer, the risk of punch-through failures may increase as a result.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.